High Surf in Hawaii, January 28 to 31, 2017

Area Forecast Discussion
National Weather Service Honolulu HI
945 AM HST Sat Jan 28 2017

.SYNOPSIS...
A cold front from the northwest will reach Kauai this afternoon,
then advance through rest of the island chain through Sunday,
bringing some clouds and showers. A breezy, cool and dry north to
northeast flow will spread across the state behind the front. A
stable and somewhat cool and dry trade wind flow is expected early
next week as a high pressure passes north of the state. Winds will
decrease and shift southerly late Wednesday and Thursday as
another front approaches the state toward the next weekend.

&&

.DISCUSSION...
No significant changes to the forecast philosophy this morning.
The approaching cold front remains northwest of the main Hawaiian
islands, and is still expected to reach Kauai this afternoon, and
then move down the island chain through Sunday. The front will
being some clouds and showers to the islands, but at this time we
aren't expecting any hydrological issues with the event. The rain
with the front will be focused over the windward and north facing
mountains, with some showers spilling over to leeward areas.

The bigger issue with this front will be the increase in winds
behind the front. This is due in part to the dry and stable
airmass behind the front. Winds are expected to peak near wind
advisory levels, which is lower than the warning levels
experienced during the event about a week ago. Winds will increase
Sunday, but for many areas peak on Monday near advisory levels. With
the dry and stable airmass behind the front, dewpoints will fall
into the 50s, making the air more noticeably cooler.

Winds will begin to turn more northeasterly on Monday, with a
moderate to locally breezy trade wind pattern in place Tuesday and
Tuesday night as a high pressure system passes north of the
state. Expect rainfall amounts during this time to remain on the
lighter side, since the drier airmass will remain overhead.

Another front will approach the state later part of next week. The
GFS and ECMWF are still in good agreement that winds will steadily
decrease on Wednesday then shift southerly by Thursday as the
advancing front drives the another ridge near the islands. The
airmass near the islands is expected to become more unstable, so
we could see a few more showers. However, the southerly winds
could draw up some volcanic emissions to the smaller islands.

&&

.AVIATION...
VFR conditions will continue across the state through the rest of
this morning and through the midday hours, as a dry and stable
airmass remains in place ahead of an approaching front. A few
light showers will be possible along with isolated MVFR conditions
over windward slopes, but no AIRMETs are expected during this
period.

The front is forecast to move across Kauai during the mid to late
afternoon, Oahu this evening, Maui County late tonight into early
Sunday morning, and the Big Island on Sunday into Sunday evening.
This front will bring a period of lower ceilings and visibilities
in moderate showers. Mountain obscuration will become likely as
the front moves through, with AIRMET Sierra probably becoming
necessary. Increasing winds behind the front will generate at
least moderate low-level turbulence beginning late this afternoon
or early this evening on Kauai, spreading across the remainder of
the state tonight into Sunday morning. Therefore AIRMET Tango will
also likely be required. With the strong winds and lowering
inversion heights, we may also see localized severe turbulence in
some areas through much of the day on Sunday.

&&

.MARINE...
A large northwest swell building this morning, will peak this
evening on Oahu. Surf from this swell will remain well above the
advisory level along north and west facing shores of the smaller
islands into Sunday. A larger swell from a more northerly
direction will build Sunday and Sunday night, then gradually
subside. Surf from this swell will reach warning levels along
north and west facing shores of the smaller islands Sunday night.
The swell will shift out of the north northeast Monday night and
Tuesday. As the swell direction shifts, east facing shores,
including east facing shores of the Big Island may get surf above
the 15 foot warning level.

A small to moderate size northwest swell is on tap for the
Wednesday through Friday time period. Finally, an east swell will
keep surf elevated on east facing shores, especially Sunday
through Tuesday, when heights may rise to near advisory level.

Winds over the coastal waters will remain below the 25 kt Small
Craft Advisory (SCA) threshold today, but the building northwest
swell will cause seas to exceed the 10 foot Small Craft Advisory
threshold over waters exposed to the swell. Winds will strengthen
starting tonight as a front moves over the Kauai waters this
evening and pushes down past the Big Island Sunday night. Winds
will reach near-gale strength in the windier areas on Sunday and
could even reach gale force on Monday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Sunday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Big Island Windward Waters.

&&

DISCUSSION...M Ballard
AVIATION...Powell
MARINE...Donaldson